Automatic retractable lancet assembly

ABSTRACT

An automatic retractable lancet assembly includes a housing with a sharp-pointed lancet movably mounted therein. A depressible plunger and slide mechanism actuates the movement of the lancet outwardly from the housing. After this outward movement is completed, the actuator elements become dissociated from further movement of the lancet. Subsequently, the lancet is automatically retracted back inside the housing by virtue of a spring element.

This is a division, of application Ser. No. 322,344, filed 11/18/81 nowabandoned, which is a continuation-in-part application of applicationSer. No. 246,523, filed Mar. 23, 1981, now U.S. Pat. No. 4,388,925.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lancet assembly, and moreparticularly, concerns an automatic retractable lancet assembly usefulin penetrating the skin of a patient.

2. Description of the Prior Art

Sharp-pointed lancets are employed to make a quick puncture orpenetration of the patient's skin in order to provide a small outflow ofblood. Various tests may be employed with only small amounts of blood sothat the blood flowing from a finger prick is normally sufficient.However, due to the sensitive nerve endings in the finger tip area, thisprocedure could induce a significant amount of pain in the patient eventhough the skin puncture produces minimal cutting. In order to minimizepotential pain, it is desirable to make the thrust of the lancet throughthe patient's skin rapidly.

Spring-loaded lancets of different types and forms have been well knownand are typified, for example, by U.S. Pat. Nos. 55,620; 1,135,465;3,030,959; 4,139,011; 4,203,446; 4,230,118; Swedish Pat. No. 124247 andSutor, A. H., et al., "Bleeding From Standardized Skin Punctures:Automated Technique for Recording Time, Intensity and Pattern ofBleeding," A. J. C. P., Volume 55, May 1971.

U.S. Pat. No. 4,203,446, above, is significant in that it teaches thepuncture of the skin of a patient with a lancet which is retracted backinto the device after piercing the patient's skin. In the patenteddevice, the downward motion of the lancet is initiated by the impact ofa spring-loaded hammer, and as this motion continues, the springpotential decreases. At the time of impact, the return spring begins tocompress and increase potential energy. When the potential energy in thereturn spring under compression exceeds the potential energy in thedriving spring, compression of the return spring ends and decompressionbegins. This, then, reverses the motion of the lancet. However, impactis necessary to compress the return spring and increase its potentialenergy rapidly. Without the impact force, the spring forces wouldapproach equilibrium and then there would be no reverse motion in orderto retract the lancet out of the patient's skin. Furthermore, sincespring potential is critical in this patented device, a conical springis relied upon to overcome recoil due to the surge of the larger returnspring. Despite the foregoing inventions, improvements in this field oflancets are still being sought.

SUMMARY OF THE INVENTION

An automatic retractable lancet assembly of the present inventioncomprises a housing with a sharp-pointed lancet movably mounted therein.Actuating means moves the lancet outwardly from the housing andthereafter becomes dissociated from further movement of the lancet.Subsequent to this outward movement of the lancet, operable means isprovided for automatically retracting the lancet back inside thehousing.

In the preferred embodiment of the present invention, the housingincludes an aperture with the lancet mounted in the housing so that itspoint lies adjacent the interior side of the aperture. A depressibleplunger is movably mounted in the housing in the end thereof oppositefrom the lancet. Also mounted inside the housing is a first spring in acompressed condition adapted to decompress upon the plunger beingdepressed into the housing. This causes the movement of the lancetoutward of the aperture for penetration of the skin of a patient. Thefirst spring is adapted to become dissociated from the lancet after thelancet completes its outward movement. A second spring is mounted insidethe housing in a substantially decompressed condition before the plungeris depressed. This second spring is adapted to become compressed duringoutward movement of the lancet. Furthermore, the second spring isadapted to decompress when the first spring becomes dissociated from thelancet. This causes the lancet to be automatically retracted back insidethe housing.

In accordance with the principles of the present invention, the desiredfunctions are achieved by virtue of structure which is notably differentfrom the structure of prior art lancet assemblies. In particular, and inthe preferable embodiment, two springs are employed to complete theintended purpose of the lancet. The first spring serves as a drivingspring to rapidly thrust the lancet outwardly for penetration of thepatient's skin. At this time, this driving spring becomes dissociatedfrom movement of the lancet. The second spring serves as a returnspring, operable after the driving spring has become so dissociated.Therefore, when the second or return spring automatically retracts thelancet back into the housing, there is no opposing spring force, such asfound in U.S. Pat. No. 4,203,446. Thus, in the present invention, thevarious spring potential energies do not have to balance as in theaforementioned patented invention. The return spring of the presentinvention only has to be sufficiently strong to retract the lancetinwardly. Therefore, considerations of balancing spring forces, as inthe previous inventions, have been obviated by the structure of thepresent invention. This allows the design of the present invention toinclude a greater liberality as far as spring sizes and strengths areconcerned. Advantageously, the present invention provides a quick thrustof the lancet outwardly to penetrate the skin of the patient, and thenautomatically retracts the lancet from the patient's skin so that dwelltime therein is minimized. It is intended that this embodiment of thepresent invention can be economically fabricated so that it can bediscarded after single use in disposable fashion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating the preferred embodiment ofthe automatic retractable lancet assembly of the present invention;

FIG. 2 is an exploded assembly plan view of the elements of theautomatic retractable lancet assembly of FIG. 1;

FIG. 3 is an enlarged end view of the slidable sleeve element takenalong line 3--3 of FIG. 2;

FIG. 4 is an enlarged end view of the slidable sleeve element takenalong line 4--4 of FIG. 2;

FIG. 5 is an enlarged end view of the skirt element of the preferredinvention taken along line 5--5 of FIG. 2;

FIG. 6 is an enlarged end view of the depressible plunger element of thepreferred invention taken along line 6--6 of FIG. 2;

FIG. 7 is a cross-sectional view of the automatic retractable lancetassembly taken along line 7--7 of FIG. 1 illustrated in position inconjunction with a finger of a patient;

FIG. 8 is a cross-sectional view of the lancet assembly of FIG. 7illustrating the sequential operation of the assembly to penetrate thefinger of the patient;

FIG. 9 is a cross-sectional view of the lancet assembly of FIGS. 7 and 8illustrating the next sequential operative step after the lancet hasbeen automatically retracted back into the assembly after the finger ofthe patient has been penetrated;

FIG. 10 is a cross-sectional view of an alternate embodiment of thelancet assembly of the present invention illustrating the assembly in apre-loaded condition;

FIG. 11 is a side view of the lancet assembly of FIG. 10;

FIG. 12 is a cross-sectional view of the lancet assembly of FIG. 10illustrated in the loaded condition for use;

FIG. 13 a cross-sectional view of the lancet assembly of FIG. 10illustrating the assembly after it has been fired with the lancet pointin position to penetrate the skin of a patient;

FIG. 14 is a cross-sectional view of the lancet assembly of FIG. 10illustrating the lancet retracted back inside the assembly after use;

FIG. 15 is a cross-sectional view of another alternate embodiment of thelancet assembly of the present invention illustrating the assembly in aloaded position before use;

FIG. 16 is a side view of the lancet assembly of FIG. 15;

FIG. 17 is a cross-sectional view of the lancet assembly of FIG. 15illustrating the assembly after it has been fired with the lancet pointin position for penetration of the skin of a patient;

FIG. 18 is a cross-sectional view of the lancet assembly of FIG. 15illustrating the lancet retracted back inside the assembly after it hasbeen used;

FIG. 19 is a cross-sectional view of another alternative embodiment ofthe lancet assembly of the present invention illustrating an alternativespring construction to the embodiment of FIG. 15;

FIG. 20 is a cross-sectional view of still another alternativeembodiment of the lancet assembly of the present invention illustratingthe assembly in a loaded condition for use;

FIG. 21 is a cross-sectional view of the lancet assembly of FIG. 20illustrating the assembly after it has been fired with the lancet pointin position for penetration of the skin of a patient;

FIG. 22 is a cross-sectional view of the lancet assembly of FIG. 20illustrating the lancet retracted back inside the assembly after use;

FIG. 23 is a side view of another alternative embodiment of the lancetassembly of the present invention;

FIG. 24 is a cross-sectional view taken along line 24--24 of FIG. 23illustrated in a pre-loaded condition;

FIG. 25 is a cross-sectional view of the lancet assembly of FIG. 23illustrating the assembly in a loaded position before use;

FIG. 26 is a cross-sectional view of the lancet assembly of FIG. 23illustrating the assembly after it has been fired with the lancet pointin position for penetration of the skin of a patient;

FIG. 27 is a cross-sectional view of the lancet assembly of FIG. 23illustrating the lancet retracted back inside the assembly; and

FIG. 28 is an opposite side view of the lancet assembly of FIG. 23.

DETAILED DESCRIPTION

While this invention is satisfied by embodiments in many differentforms, there is shown in the drawings and will herein be described indetail a preferred embodiment of the invention, with the understandingthat the present disclosure is to be considered as exemplary of theprinciples of the invention and is not intended to limit the inventionto the embodiment illustrated. The scope of the invention will bemeasured by the appended claims and their equivalents.

Referring to the drawings, and FIGS. 1 and 2 in particular, there isillustrated a preferred embodiment of an automatic retractable lancetassembly 20. As more clearly seen in FIG. 2, taken in conjunction withFIG. 1, the basic components of lancet assembly 20 are the following: ahousing 22, a lancet 24, a first spring 26, a second spring 28, adepressible plunger 30, a skirt 32 and a slidable sleeve 34. In thisembodiment being described, all of the aforementioned elements arepreferably cylindrically shaped and designed for coaxial arrangementwith each other as described below.

More specifically, housing 22 is an elongate hollow tube having apassageway 36 therethrough terminating in an opening 38 at its proximalend and an aperture 39 at its distal end. An annular flange 40 surroundsopening 38 for structural purposes in maintaining the elements togetherwhen assembled. In this particular embodiment, there are threelongitudinal slots 41 (only two being shown in FIG. 2 since they arespaced approximately 120° apart) through the peripheral wall of housing22. These slots terminate toward the distal end of the housing atslanted, inclined surfaces 42.

Lancet 24 includes a sharp point 44 extending from a slidable piston 46.As more clearly seen in FIG. 7 which represents the instant invention inthe assembled condition before use, lancet 24 is slidably positionedinside passageway 36. The diameter of piston 46 is designed to slidewithin the inside diameter of passageway 36 of housing 22. Sharp point44 faces toward aperture 39 and is maintained inside the housingadjacent the interior side of aperture 39. Second spring 28 is providedto maintain the lancet in this position. Spring 28 is basically a coilspring which fits around the sharp point of the lancet so that piston 46rests upon this spring. An inwardly projecting lip 48 at the distal endof the housing cooperates to hold the spring inside the housing. In thisposition as seen in FIG. 7, which represents the lancet assembly beforeuse, spring 28 is in a substantially decompressed condition.

Slidable sleeve 34 is adapted to slide over housing 22 in coaxialfashion. This sleeve includes three flexible legs 50 spacedapproximately 120° apart, as illustrated in FIGS. 3 and 4, and adaptedto correspond to slots 41 of the housing. Each flexible leg includes aninwardly projecting foot 51 which projects through corresponding slot 41in the housing. As seen in FIG. 7, feet 51 engage the top of piston 46of the lancet. This engagement helps maintain the lancet in a relativelyimmobile position in the pre-use condition.

Skirt 32, also preferably cylindrically shaped, includes an upperportion 54 which is sized to snugly fit around flange 40 of the housing.The bottom portion of skirt 32 includes three flexible arms 55 extendingdownwardly, as seen in FIG. 5. Each arm 55 has at its distal end a hook56 projecting inwardly. In the assembled condition as seen in FIG. 7,skirt 32 is oriented so that arms 55 are peripherally offset from legs50 of the slidable sleeve. In this manner, hooks 56 fit between legs 50and engage the flat surfaces 58 on the sleeve between the legs. Thisimmobilizes slidable sleeve in a relatively fixed condition before thelancet assembly is used. In this condition, first spring 26 iscompressed between the proximal end of slidable sleeve 22 and flange 40of the housing. First spring 26 is essentially similar to second spring28 inasmuch as it is a coil spring. This first spring is, however,larger in diameter and should be designed with a larger spring forceinasmuch as it is the driving spring for rapidly thrusting the lancetthrough the skin of the patient. With the hooks at the end of the skirtengaging the flat surfaces of the slidable sleeve, first spring 26 iseffectively maintained in the compressed condition before use of thislancet assembly, as more clearly seen by referring to FIG. 7.

Depressible plunger 30 is preferably a cylindrically shaped plug with aflat push-button surface 60 at its proximal end. Depending from thedistal end of plunger 30 are three equally spaced flexible arms 61, asillustrated in FIG. 6. Plunger 30 is slidably positioned inside housing22 in the end opposite from the lancet so that flexible arms 61 projectthrough slots 41 running along the longitudinal axis of the housing. Inaddition, flexible arms 61 also project through slots 62 which runlongitudinally in the proximal portion of slidable sleeve 34 asillustrated in FIG. 4. Slots 62 are oriented to correspond with theorientation of slots 41 in the housing. Slots 62 terminate distally inslanted, inclined surfaces 64 which can be seen in FIG. 7. In the loadedcondition before use, flexible arms 61 of the plunger may either contactinclined surfaces 64 or be slightly spaced therefrom. In either case,the flexible arms of the plunger are adapted to engage the inclinedsurfaces on the slidable sleeve when the plunger is downwardlydepressed. FIGS. 1 and 7 illustrate the automatic retractable lancetassembly of the present invention in the loaded condition as it wouldappear before use. In FIG. 7, a finger F of the patient is positionedadjacent the distal end of the assembly just before use so that thefinger covers aperture 39. The operation of this lancet assembly,illustrating penetration of the skin of the finger and then automaticretraction of the lancet is seen in FIGS. 8 and 9.

Turning to FIG. 8, in particular, lancet assembly 20 is shown inposition on top of finger F of a patient, while the finger of theoperation OF is illustrated pushing downwardly on depressible plunger30. This downward movement causes flexible arms 61 of the plunger toengage inclined surfaces 64 on the slidable sleeve. Inasmuch as hooks 56of the skirt maintain the slidable sleeve in a fixed position, contactof flexible arms 61 against inclined surfaces 64 causes the arms to flexoutwardly. This outward flexure causes contact with flexible arms 55 ofthe skirt. In turn, flexible arms 55 flex outwardly a sufficient amountso that hooks 56, at the end of flexible arms 55, become disengaged fromflat surfaces 58 on the slidable sleeve. Once this disengagement occurs,there is no force tending to compress spring 26 into the compressedcondition. As a result, with the restraining force removed, the springis released causing an expansion of the spring. This expansion causessleeve 34 to move distally within housing 22 in a rapid thrustingmovement. Inasmuch as feet 51 at the distal end of the sleeve are inengagement with the piston portion of lancet 24, the lancet also movesdistally. Sharp point 44 moves rapidly out of aperture 39 and penetratesfinger F positioned just under the aperture. While this is occurring, itis noted that the distal movement of lancet 24 has caused second spring28 to become compressed. This compression is a direct result of theenergy transmitted to slidable sleeve 34 by the release of first spring26. In order to assure proper compression of second spring 28, it isdesirable that the first or driving spring have a higher spring constantthan the second or return spring.

In addition to causing downward movement of lancet 24 and compression ofsecond spring 28, the downward or distal movement of slidable sleeve 34causes flexible legs 50 to engage inclined surfaces 42 on housing 22. Asa result, the downward movement of flexible legs 50 against inclinedsurfaces 42 causes these flexible legs to flex outwardly. As aconsequence, inwardly projecting feet 51 become disengaged from thepiston portion of lancet 24. This condition is more clearly seen byreferring to FIG. 9. Inasmuch as feet 51 serve as the restraining forceagainst second spring 28 when compressed, the disengagement of thesefeet from the lancet effects a release of this spring. This in turncauses an expansion of spring 28 thereby rapidly retracting lancet 24back inside the housing. It is noted that when spring 28 expands itsentire energy is transmitted only to lancet 24 to effect its retractionback inside the housing. With feet 51 disengaged, slidable sleeve 34also becomes dissociated from the retraction movement of the lancetcaused by expansion of second spring 28. Therefore, when second spring28 expands, it is not working against the decompressed state of firstspring 26 since the disengagement of feet 51 dissociate the entireslidable sleeve and first spring 26 from the retraction movement of thelancet and the decompression of second spring 28. Accordingly, with alow amount of energy required to retract the lancet back inside thehousing, second spring 28 can be a small lightweight and inexpensivespring. It is appreciated that the structure of the present lancetassembly causes not only the rapid thrusting movement of the lancet topenetrate the skin of the patient, but also effects the automaticretraction of the lancet back inside the housing of the assembly. Thus,downward depression of plunger 30 is the stimulus for both outwardrelease and inward retraction of the lancet. Insofar as a preferredembodiment of the present invention is intended to be disposable, thehousing, slidable sleeve, flexible skirt and depressible plunger can befabricated of inexpensive plastic materials. On the other hand,lightweight metals can be employed for the lancet and the two springsdescribed above.

Turning now to the embodiment illustrated in FIGS. 10-14, lancetassembly 70 is comprised of a relatively flat housing 71 which may befabricated in two parts for ready assembly. Inside housing 71 is a firstblock 72 to which two springs are connected: a first preferably flatcoil spring 74 and a second also preferably flat coil spring 75. Both ofthe coil springs preferably have a plurality of compressible folds lyingsubstantially along a flat plane inside housing 71, although spring 74preferably has a higher spring constant than spring 75. Connected to theother end of flat spring 75 is a lancet block 76. At the distal end oflancet block 76 is a sharp pointed lancet 78. It is preferred thatsprings 74 and 75, block 72 and lancet block 76 be fabricated as anintegral, unitary structure. For example, and while other materials maybe used, the composite structure of springs, and two blocks, may be madeof plastic material with the flat springs being very thin and thushighly resilient in nature. Lancet 78 at the distal end of lancet block76 is preferably made of metal to facilitate penetration of the skin ofa patient.

FIG. 10 depicts lancet assembly 70 in a relaxed, or preloaded condition.In FIG. 10, there is no compression on either of the springs. Lancetblock 76 is partially positioned in bore 79 at the distal end of housing71. Bore 79 terminates in an aperture 80 at the distal end of thehousing. Block 72 is adapted to slide inside the interior of housing 71and is dimensioned accordingly. Block 72 includes a notch 81 partiallycut from its body so that a depressible button 82 may be engagedtherein. Button 82 is preferably a cut-out portion of housing 71 adaptedto pivot for example, on a living hinge (not shown) formed in housing71.

Turning now to FIG. 12, lancet assembly 70 is loaded by pressinginwardly on flange 84 at the top of a slidable plunger 85. Connected toplunger 85 inside housing 71 is a slidable piston 86. It can be seen inFIG. 12 that when plunger 85 is depressed inwardly, piston 86 compressesspring 74. Block 72 remains stationary due to the fact that depressiblebutton 82 is engaged in slot 81. Plunger 85 is depressed through opening88 in the top of the housing so that the pair of resilient arms 89 alsopasses through opening 88. Once the arms are inside the interior of thehousing, their resilient nature causes them to resiliently deflectoutwardly beyond the diameter of opening 88. Therefore, once plunger 85is depressed to load the lancet assembly, it cannot be readily reloaded,thereby preventing inadvertent reuse. This feature contributes to thedisposable nature of the lancet assembly being discussed.

In the loaded condition for firing, spring 74 is under compression,whereas spring 75 remains in the relaxed condition. Referring now toFIG. 13, depressible button 82 is pushed at its lower end (as indicatedby the arrow) so that the button becomes disengaged from slot 81 inblock 72. This immediately releases the compression on spring 74 andcauses block 72 to move distally in the direction toward aperture 80.However, a pair of abutment stops 90 inside housing 71 limits the travelof block 72 after the tension in spring 74 has been released. When block72 strikes stops 90, the weight of lancet block 76 causes spring 75 tostretch and become biased due to its resilient nature. When this occurs,lancet block 76 slides through bore 79 until lancet 78 emerges outwardof aperture 80. A shoulder 91 inside the housing also limits the travelof lancet block 76 through bore 79 so that the emergence of lancet 78can be controlled. Penetration of the skin of a patient would occur atthis step of the utilization of lancet assembly 70.

The occurrence depicted in FIG. 13, it is understood, is only momentarydue to the characteristics of spring 75. As illustrated in FIG. 14,spring 75 has returned to its normal relaxed condition, at the same timeretracting lancet block 76, with lancet 78, back inside housing 71. Itis understood that the retraction mechanism of spring 75 is independentof any action of spring 74. This is due to the fact that once spring 74is relaxed after being compressed, it is no longer associated withmovement of lancet 78. Therefore, when spring 75 returns back to itsrelaxed condition it is not balancing any spring force remaining inspring 74, but is merely acting independently. The action of spring 75to return to its relaxed condition, therefore automatically retracts thelancet back inside the housing. The entire sequence to release thelancet and retract same occurs very quickly so as to minimize trauma tothe patient. It can be seen by referring to FIG. 14, that once thelancet is retracted back inside the housing, the assembly cannot bereused and is therefore ready to be disposed.

While not shown in the drawings, the embodiment of FIG. 10 may beprepackaged in the loaded condition, i.e., spring 74 may be assembledinto housing 71 so that it is already compressed and under tension. Thiswould, of course, eliminate the need for the loading mechanism such asdepressible plunger 85. The remaining elements and features of apre-loaded lancet assembly could be essentially the same as thoseelements and features previously described.

Another embodiment of a lancet assembly employing the principles of thepresent invention is illustrated in FIGS. 15-18. Referring to FIGS. 15and 16, in particular, lancet assembly 100 includes a housing preferablyof a generally flat nature which may be formed in two separable piecesfor ready assembly of the components therein. Housing 101 includes anaperture 102 in one end thereof. It is preferred that housing 101 beformed with a number of integral resilient spring members. Inparticular, a coiled flat spring 104 is formed inside one end of housing101. At the other end of housing 101, a pair of leaf springs 105 extendinwardly from aperture 102. The coiled and leaf springs, along with thehousing, are preferably formed of plastic material so that they may bereadily molded. The thickness and shape of the aforementioned springs isdesigned to impart resiliency thereto.

Positioned inside housing 101 is a slidable plunger 106. The upperportion of plunger 106 is sized to slidably fit inside housing 101,whereas the lower portion of plunger 106 is dimensioned to slidably fitbetween leaf springs 105, which lie substantially parallel to the axisof movement of the plunger. At the distal end of plunger 106 is mounteda sharp pointed lancet 108. A post 109 extends outwardly from the flatsurface of housing 101 so that plunger 106 can be loaded for firing, ifthe lancet assembly is assembled with the internal springs in a relaxedcondition. To load the lancet assembly, the user pushes upwardly on post109 until an undercut notch 110 mates with a hook 111 extending throughthe side wall of housing 101. When notch 110 and hook 111 are mated, theupper portion of plunger 106 compresses coiled flat spring 104 andplaces it in tension. At this time, lancet 108 lies adjacent theinterior side of aperture 102. To fire lancet assembly 100, the userpushes inwardly on button 112 which is connected to hook 111. Inwardmovement of hook 111 causes it to become disengaged from notch 110. Dueto the tension on coil spring 104 which is released, plunger 106 israpidly urged in the direction toward aperture 102. The rapid movementof plunger 106 causes lancet 108 to emerge outward of aperture 102. Atthe same time, inclined surfaces 114 on plunger 106 engage the uppersurfaces of leaf springs 105. As can be seen in FIG. 17, such contact bythe plunger causes leaf springs 105 to deflect outwardly at the sametime lancet 108 emerges from aperture 102. In this regard, deflection ofleaf springs 105 momentarily biases them under tension. This tensioncauses leaf springs 105 to return back to their original, relaxedcondition. This, in turn, pushes plunger 106, with lancet thereon, backinside housing 101. This sequential step is illustrated in FIG. 18. Itcan be seen that leaf springs 105 have returned to their relaxed, normalcondition thereby automatically retracting lancet 108 back insidehousing 101. As in the previously described embodiments, the action ofthe leaf springs to retract the lancet back inside the housing takesplace independently of coil spring 104. It can be seen in both FIGS. 17and 18, that the relaxation of the tension from coil spring not onlycauses the plunger to slide toward the aperture, but also completelydisengages the plunger from the flat coiled spring. Therefore, allmovement of the plunger back inside the housing after the lancetpenetrates the skin of the patient is caused solely by leaf springs 105.There is, thus, no balancing of spring forces required by the structureof this embodiment of the lancet assembly.

The embodiment of FIGS. 15-18 may be slightly modified as illustrated inFIG. 19. Lancet assembly 100a has a coiled flat spring including aplurality of folds therein. The spring constant of the coiled flatspring can thus be modified according to the number of folds formedtherein. All other elements of lancet assembly 100a are substantially asdescribed above with respect to FIGS. 15-18.

Instead of the coiled springs as described in the two previousembodiments, a different spring arrangement may be utilized asillustrated in the embodiment of FIGS. 20-22. As seen in FIG. 20, lancetassembly 120 includes a housing 121 which is preferably generally flatand may be comprised of two or more portions for ready assembly. It ispreferred that lancet assembly 120 be fabricated with two integrallyformed leaf springs, 122 and 124. These leaf springs are desirablyconnected to the housing so that they extend over a substantial lengthinside the housing to assure that sufficient resiliency is provided. Aplunger 125 is mounted inside housing 121 on one or more tracks 126.Further, plunger 125 has its distal end slidably positioned in a bore128 extending through housing 121. Bore 128 terminates in an aperture129. At the distal end of plunger 125 a sharp pointed lancet 130 ismounted.

Plunger 125 is formed with an undercut notch 131 which is adapted tomate with a preferably frangible hook 132 depending from a wall ofhousing 121. A slidable button is mounted adjacent hook 132 andpreferably includes a sharp pointed slidable rod 135 directed toward thebend in hook 132. In addition, plunger 125 includes a downwardlydepending flange 136 which is adapted to contact leaf spring 124 ashereinafter described. In the loaded condition for firing, plunger 125is retained in position by the mating of the previously described hookand notch in a latched arrangement. In this instance, as seen in FIG.20, leaf spring 122 engages the proximal end of the plunger and isplaced under tension. No contact is being made at this time with leafspring 124.

To use lancet assembly 120, the operator presses inwardly on button 134so that sharp pointed rod 135 readily fractures hook 132 due to itsfrangible nature. This causes a release of the tension on leaf spring122 which rapidly returns to its normal, relaxed position as seen inFIG. 21. At the same time, plunger 125 is urged rapidly in the directiontoward aperture 129 until lancet 130 emerges therefrom. Tracks 126 maybe positioned to control the distance which lancet 130 travels outwardof aperture 129.

By the time the lancet extends out of the aperture, downwardly dependingflange 136 on the plunger has come in contact with leaf spring 124causing the leaf spring to deflect and be placed under tension. As inthe previously described embodiments, the bias of leaf spring 124 ismomentary since it rapidly returns back to its normal, relaxed positionas seen in FIG. 22. Return of leaf spring 124 to its normal positioncauses lancet 130 to be automatically retracted back inside housing 121.Retraction of lancet 130 back inside the housing is done independentlyby leaf spring 124. Inasmuch as leaf spring 122 has become disengagedfrom contact with plunger 125 after its tension was released, it is onlythe action of leaf spring 124 which causes the retraction of the lancetback inside the assembly. Therefore, there is no balancing of springforces against each other in the firing of the lancet for penetration ofthe skin of a patient and its automatic retraction back inside theassembly.

Referring now to the embodiment illustrated in FIGS. 23-28, assembly 200comprises a lancet holder 210 with a projecting lift-pin 212, mainspring 211, retraction spring 213 and lancet 214. This configuration ismore clearly seen by referring specifically to FIGS. 23 and 24. Lancetholder 210 is designed to travel in a housing 215 along sides 216 and isheld in position by lift-pin 212 bearing on edge 217 of housing slot218. Main spring 211 and the significantly lighter and smallerretraction spring 213 are in the normal or relaxed state. Lancet 214 isheld in position interiorly of aperture 219.

Turning to FIG. 25, assembly 200 is illustrated in a loaded condition.Lancet holder 210 has been raised upwardly on sides 216 by the lift-pin212 and is held in the position shown by latch 220 bearing against notch221 of the lance holder. Latch 220 is preferably an integral hinge thatis molded as part of housing 215. Main spring 211 is compressed andlancet 214 has been moved to a new upward position from aperture 219.Retraction spring 213 remains in the normal or uncompressed condition.

As seen in FIG. 26, latch 220 has been pushed in the direction of thearrow to release lancet holder 210. Spring 211 returns to itsuncompressed condition and lancet holder 210 is projected downwardly inhousing 215 until it abuts against stop 222 which is formed in thehousing. During this motion lift-pin 212 is sheared off by sharp edge217 of the slot. Thus, the invention cannot be reloaded and inadvertentreuse is prevented; this feature further contributes to the disposablenature of the invention. When lancet holder 210 contacts stop 222,retraction spring 213 becomes compressed and lancet 214 passes throughaperture 219 to penetrate the patient's skin. The travel of the lancetholder is limited by the position of stop 222. This effectively controlsthe depth of penetration of the patient's skin by the lancet.

In FIG. 27, the assembly is illustrated immediately following theretraction of lancet 214 inside the housing. Retraction spring 213 hasextended and lancet holder 210 has been withdrawn. Retraction spring 213is preferably a light spring because the lance holder is completelydissociated from the main spring following the extension or return tonormal state of main spring 211. Therefore, the retraction spring servesonly to withdraw the unrestrained lancet holder, as in the previouslydescribed embodiments.

Thus, there has been provided in accordance with the present inventionan automatic retractable lancet assembly. While two springs arepreferably employed, the return spring operates independently and isdissociated from any movement of the driving spring. Accordingly,balance of spring forces is not required as in prior art lancetassemblies. This allows more straightforward operation, reduction ofspring sizes and lighter weight materials.

What is claimed is:
 1. An automatic retractable lancet assemblycomprisinga housing having an aperture; a lancet mounted for movement insaid housing with its point lying substantially adjacent the interiorside of said aperture; a first spring mounted inside said housing in asubstantially relaxed condition and adapted to be compressed in a biasedcondition and further adapted to decompress upon release to cause themovement of said lancet point outward of said aperture for penetrationof the skin of a patient; said first spring adapted to becomedissociated from further movement of said lancet after said lancetcompletes its outward movement; actuating means for compressing saidfirst spring into a biased condition; latching means connected to saidactuating means for retaining said first spring in said biased conditionuntil use; release means slidable through said housing for releasingsaid first spring from its biased condition; said release meansincluding a sharp point for permanently severing said latching means; asecond spring inside said housing in a substantially relaxed conditionbefore said first spring is released and adapted to become biased whensaid first spring becomes dissociated from further movement of saidlancet to cause said lancet point to be automatically retracted backinside said housing.
 2. The assembly of claim 1, wherein said first andsecond springs are leaf springs.
 3. The assembly of claim 2 wherein saidhousing and said springs are formed of plastic material.
 4. The assemblyof claim 2 wherein said housing and said springs are formed as anintegral, unitary structure.